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After the diffuser, the information content of the object is scrambled so that the light distribution at the pixelated sensor looks like the familiar speckle noise. Credit: Jesús Lancis/Jaume I University

July 02, 2014 10:25 AM Eastern Daylight Time

WASHINGTON--(BUSINESS WIRE)--Optical imaging methods are rapidly becoming essential tools in
biomedical science because they’re noninvasive, fast, cost-efficient and
pose no health risks since they don't use ionizing radiation. These
methods could become even more valuable if researchers could find a way
for optical light to penetrate all the way through the body's tissues.
With today’s technology, even passing through a fraction of an inch of
skin is enough to scatter the light and scramble the image.

Now a team of researchers from Spain’s Jaume I University (UJI) and the
University of València has developed a single-pixel optical system based
on compressive sensing that can overcome the fundamental limitations
imposed by this scattering. The work was published today in The Optical
Society’s (OSA)
open-access journal Optics
Express.

“In the diagnostic realm within the past few years, we’ve witnessed the
way optical imaging has helped clinicians detect and evaluate suspicious
lesions," said Jesús Lancis, the paper’s co-author and a researcher in
the Photonics Research Group at UJI. "The elephant in the room, however,
is the question of the short penetration depth of light within tissue
compared to ultrasound or x-ray technologies. Current knowledge is
insufficient for early detection of small lesions located deeper than a
millimeter beneath the surface of the mucosa."

"Our goal is to see deeper inside tissue,” he added.

To achieve this, the team used an off-the-shelf digital micromirror
array from a commercial video projector to create a set of
microstructured light patterns that are sequentially superimposed onto a
sample. They then measure the transmitted energy with a photodetector
that can sense the presence or absence of light, but has no spatial
resolution. Then they apply a signal processing technique called
compressive sensing, which is used to compress large data files as they
are measured. This allows them to reconstruct the image.

One of the most surprising aspects of the team’s work is that they use
essentially a single-pixel sensor to capture the images. While most
people think that more pixels result in better image quality, there are
some cases where this isn't true, Lancis said. In low-light imaging, for
instance, it's better to integrate all available light into a single
sensor. If the light is split into millions of pixels, each sensor
receives a tiny fraction of light, creating noise and destroying the
image.

“Something similar happens when you try to transmit images through
scattering media,” Lancis said. “When we use a conventional digital
camera to get an image, we only see the familiar noisy pattern known as
‘speckle.’ In compressive imaging, since we aren’t using pixelated
sensors, it should be less sensitive to light scrambling and enable
transmission of images through scattering.”

Also notable, the team’s technique could operate through dynamic
scattering. “Most scattering media of interest, like biological tissue,
are dynamic in the sense that the scatter centers continuously change
their positions with time -- meaning that the speckle patterns are ‘in
motion.’ This is ideal for some applications because monitoring the
changes of the speckle can reveal information about the sample, but the
drawback is that it’s a major nuisance to transmit or get images,”
Lancis pointed out. “Our technique, however, requires no calibration of
the medium, and its fluctuations during the sensing stage don’t limit
imaging ability.”

What’s ahead for the team? “Our next goal is to break the barriers of
light penetration depth inside a scattering medium with the
state-of-the-art megapixel-programmable spatial light modulators used in
consumer electronics,” Lancis says. To do this, they’ll need to
demonstrate that their technique works even when the sample is embedded
inside the tissue.

EDITOR’S NOTE: Images and video are available to members of the media
upon request. Contact Angela Stark, astark@osa.org.

About Optics Express

Optics Express reports on new developments in all fields of
optical science and technology every two weeks. The journal provides
rapid publication of original, peer-reviewed papers. It is published by
The Optical Society and edited by Andrew M. Weiner of Purdue University. Optics
Express is an open-access journal and is available at no cost to
readers online at www.OpticsInfoBase.org/OE.

About OSA

Founded in 1916, The Optical Society (OSA) is the leading professional
society for scientists, engineers, students and business leaders who
fuel discoveries, shape real-world applications and accelerate
achievements in the science of light. Through world-renowned
publications, meetings and membership programs, OSA provides quality
research, inspired interactions and dedicated resources for its
extensive global network of professionals in optics and photonics. For
more information, visit www.osa.org.